60-Second Science

Sea Otters Fight Global Warming

By controlling kelp-eating sea urchins, otters help the seaweed thrive and absorb more carbon dioxide, in a case study of the role of animals in the carbon cycle. Sophie Bushwick reports

Plants can pull carbon dioxide, the planet-warming greenhouse gas, out of Earth’s atmosphere. But these aren’t the only living organisms that affect carbon dioxide levels, and thus global warming. Nope, I’m not talking about humans. Humble sea otters can also reduce greenhouse gases, by indirectly helping kelp plants. That finding is in the journal Frontiers in Ecology and the Environment. [Christopher C Wilmer et al., Do trophic cascades affect the storage and flux of atmospheric carbon? An analysis of sea otters and kelp forests]

Researchers used 40 years of data to look at the effect of sea otter populations on kelp. Depending on the plant density, one square meter of kelp forest can absorb anywhere from tens to hundreds of grams of carbon per year. But when sea otters are around, kelp density is high and the plants can suck up more than 12 times as much carbon. That’s because otters nosh on kelp-eating sea urchins. In the mammals’ presence, the urchins hide away and feed on kelp detritus rather than living, carbon-absorbing plants.

So climate researchers need to note that the herbivores that eat plants, and the predators that eat them, also have roles to play in the carbon cycle.

—Sophie Bushwick

[The above text is a transcript of this podcast.]

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